Hitherto, so-called Ziegler-Natta catalysts comprising a titanium compound and an organoaluminum compound have been known as catalysts for producing polymers or copolymers of olefins. On the other hand, recently, a technology has been found wherein homopolymerization of ethylene or copolymerization of ethylene with other α-olefins can be performed with high activity by using catalysts comprising a so-called metallocene compound such as bis(cyclopentadienyl)zirconium dichloride and an aluminoxane which is a kind of organoaluminumoxy compounds. The details of this technology are disclosed in JP-B-4-12283 (corresponding to DE 3127133.2).
On the other hand, as catalyst systems using activators other than the organoaluminumoxy compounds, Taube et al. report in J. Organometall. Chem., 347. C9(1988) carrying out polymerization of ethylene using a compound represented by [Cp2TiMe(THF)]+[BPh4]− (Cp: cyclopentadienyl group, Me: methyl group, Ph: phenyl group, THF: tetrahydrofuran). Jordan et al. report in J. Am. Chem. Soc., 109. 4111(1987) that ethylene is polymerized using a zirconium complex represented by [Cp2ZrR(L)]+ (R: methyl group or benzyl group, L: Lewis base).
Furthermore, JP-A-1-501950 and JP-A-1-502036 disclose a method for polymerizing olefins using a catalyst comprising a cyclopentadienyl metal compound and an ionic compound capable of stabilizing a cyclopentadienyl metal cation.
In addition, JP-A-5-301917, JP-A-6-136047, JP-A-9-59310, JP-A-11-269222, etc. disclose catalyst systems using organoaluminum compounds and clays, clay minerals or ion-exchangeable laminar compounds as activators.
In general, when olefins are polymerized by using these metallocene catalysts, alkylaluminums such as triethylaluminum and triisobutylaluminum ordinarily used in Ziegler-Natta catalysts are used together with the metallocene catalysts. The alkylaluminums are the materials that serve to remove impurities in the polymerization system which become catalyst poisons, i.e. scavengers, and are added to the polymerization system in order to maintain high activity.
As methods for polymerization of olefins using the metallocene catalyst and the alkylaluminum, JP-A-3-179005 discloses polymerization of olefins in the presence of a catalyst comprising a neutral metallocene compound, an alkylaluminum and a Lewis acid, JP-A-3-207704 discloses a method of polymerization of olefins which includes mixing a metallocene catalyst prepared from a neutral metallocene compound and an ionic compound with an aluminumalkyl-olefin mixture, and JP-A-5-505838 discloses polymerization of olefins in the presence of a catalyst containing the reaction product of a group IV metal compound of bis(cyclopentadienyl) having a proton reactive substituent with a compound of a cation having a donatable proton and an activator, and a compound of a Group IIIA element.
However, as disclosed in Journal of Organometallic Chemistry 497 (1995) 55-59, in the presence of an excess amount of trimethylaluminum or triethylaluminum, the catalysts are poisoned and thus have lower polymerization activity. Therefore, there is a problem that the scavengers for displaying the activity in metallocene catalysts can be effectively used only when their concentration is in a specific narrow range and thus it is difficult to maintain the polymerization activity at a high level.
As a result of intensive research conducted by the present inventors, it has been found that when specific organomagnesium compounds are used as the scavenger, the reduction in the polymerizing activity of the catalyst does not occur regardless of the scavenger concentration, thus the high polymerizing activity of the catalyst can be maintained in a wide range of the scavenger concentration. Thus, the present invention has been accomplished.
The object of the present invention is to provide a catalyst for olefin polymerization comprising a scavenger which can maintain a high polymerization activity of the catalyst in a wide range of scavenger concentration and a method for polymerization of olefins using said catalyst, that can provide a polymer powder which does not cause any phenomena, such as deposition on the reactor during the polymerization, and has excellent particle properties.